JP6725250B2 - Front powder design method and front powder manufacturing method - Google Patents

Description

The present invention is a method of designing a front powder, and relates to a method of manufacturing a front powder.

Continuous casting is known as a method for casting molten metal. In continuous casting, molten metal (for example, molten steel) is supplied to the mold from above the mold. Here, the mold is cooled, for example, by circulating cooling water in the mold. Therefore, of the molten metal in the mold, the portion facing the mold is cooled and becomes a solidified shell. As a result, a slab is produced in which only the surface layer is solidified in the mold. Then, the slab is pulled out from the lower end of the mold. Next, the slab pulled out of the mold is further cooled while being supported and conveyed by a plurality of pairs of support rolls.

Here, in order to perform continuous casting stably, it is necessary to maintain the lubricity between the slab and the mold in a good state. Therefore, the mold powder is supplied to the mold from above the mold together with the molten metal. The mold powder is melted by the heat supplied from the molten metal in the mold to become a liquid (that is, slag is formed), and the liquid mold powder (that is, molten slag) enters between the slab and the mold. Since the mold is cooled, part of the molten slag that has entered between the slab and the mold is solidified to form a fixed layer. Such a fixed layer of mold powder controls the cooling of the slab. On the other hand, the molten slag that has not solidified maintains the lubricity between the cast piece and the mold in a good state. Further, since the molten steel surface (that is, the upper end surface of the mold) is covered with the molten slag and the unmelted mold powder, heat radiation from the molten steel surface is suppressed.

Here, the mold powder is roughly classified into a front powder supplied into the mold at the start of continuous casting and a main body powder supplied into the mold after the front powder is supplied. That is, at the start of continuous casting, a predetermined amount of front powder is supplied into the mold, and then the front powder is switched to the main body powder. Both the front powder and the main body powder have the functions described above. At the start of continuous casting (that is, when molten steel does not exist in the mold), the following processes are roughly performed. That is, the outlet of the mold is closed with a dummy bar and the nozzle is inserted into the mold. Then, the molten metal is discharged from the nozzle outlet to supply the molten metal into the mold. As a result, an initial cast piece (so-called bottom cast piece) at the start of casting is produced. After the nozzle outlet is hidden by molten steel, front powder is supplied into the mold from above the mold.

Here, the drawing speed at the beginning of casting is slow, and since the mold has not been sufficiently warmed during the production of the bottom slab, the molten steel surface is likely to solidify. The solidified material on the molten steel surface is also called Dickel. Therefore, an exothermic agent may be added to the front powder. As a result, heat generation is imparted to the front powder. When the front powder having heat generation is supplied into the mold, the front powder generates heat. Since the molten steel surface is heated by the front powder, solidification of the molten steel surface is suppressed. Further, the heat generation of the front powder also promotes the melting of the front powder itself.

Further, at the start of continuous casting, poor lubrication between the solidified shell and the mold is likely to occur. This is because the solidified shell and the mold are in direct contact with each other before the front powder is supplied into the mold. For this reason, the front powder is required to melt quickly and enter between the solidified shell and the mold. On the other hand, if the front powder melts too fast, the unmelted front powder will disappear from the molten steel surface before the main body powder is supplied. In this case, since the molten slag is exposed, the heat of the molten steel surface is radiated and excessively cooled. As a result, solidification of the molten steel surface may occur. Therefore, the melting rate of the front powder has an appropriate range. The specific range of the proper range can be changed according to various factors (for example, specifications required for the front powder), but in any case, it is extremely important to adjust the melting rate of the front powder within the proper range. ..

Patent Document 1 discloses a technique in which the solidification temperature, the melting temperature, the viscosity, and the melting speed of the front powder are set to values within appropriate ranges. Further, Patent Document 1 discloses that the content of Ca-Si alloy and iron oxide is set to a value within a predetermined range as a guideline for setting the melting rate of the front powder to a value within an appropriate range. .. Here, Ca-Si alloy is an example of an exothermic agent, and iron oxide is an example of an exothermic agent. The exothermic aid is a material that promotes oxidation of the exothermic agent. Therefore, in Patent Document 1, the melting rate of the front powder is adjusted by adjusting the contents of the exothermic agent and the exothermic aid.

Patent Document 2 discloses a technique of adjusting the melting rate of the mold powder by adding a melting rate adjusting agent to the mold powder. Specifically, Patent Document 2 discloses a mathematical formula showing a correspondence relationship between the mass% of each component constituting the melting rate adjusting agent and the melting rate of the mold powder. And in patent document 2, the mass% of each said component is adjusted so that the melting rate of mold powder may become a value within an appropriate range.

JP, 10-5953, A JP, 2003-53497, A

Further, in recent years, there has been a strong demand for adjusting the melting rate of the front powder to a specific target melting rate. In this regard, it is certainly disclosed in Patent Document 1 that the contents of the Ca-Si alloy and the iron oxide are set to values within a predetermined range as a guideline for setting the melting rate of the front powder within the appropriate range. Has been done. Therefore, by setting the contents of the Ca-Si alloy and the iron oxide within the predetermined range, it can be expected that the melting rate of the front powder becomes any value within the proper range. However, Patent Document 1 does not disclose or suggest any guideline for setting the melting rate of the front powder to a specific target melting rate. Therefore, with the technique disclosed in Patent Document 1, it is not possible to adjust the melting rate of the front powder to a specific target melting rate.

On the other hand, Patent Document 2 discloses a mathematical formula showing the correspondence relationship between the mass% of each component constituting the melting rate adjusting agent and the melting rate of the mold powder. Therefore, according to the technique disclosed in Patent Document 2, it is expected that the melting rate of the mold powder reaches a specific target melting rate by appropriately adjusting the mass% of the SiC powder or the like. When the technique disclosed in Patent Document 2 is applied to the front powder, the same effect can be expected for the front powder. However, if the technique disclosed in Patent Document 2 is applied to the front powder, it becomes necessary to add a melting rate adjusting agent to the front powder separately. Therefore, another problem that the manufacturing cost of the front powder increases increases. Therefore, the technique disclosed in Patent Document 2 cannot fundamentally solve the above-mentioned problem.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to adjust the melting rate of the front powder to a specific target melting rate at low cost, which is new and An object of the present invention is to provide an improved front powder design method, front powder manufacturing method, and front powder.

In order to solve the above problems, according to an aspect of the present invention, there is provided a method for designing a front powder containing a heat-generating agent and a heat-generating agent for oxidizing the heat-generating agent, which is a mass ratio of the heat-generating agent and the heat-generating agent. Corresponding to the target melting rate of the front powder, and the step of specifying the range of the exothermic agent/heating auxiliary agent ratio as a linear region when the correspondence relationship between the exothermic agent/heating auxiliary agent ratio and the melting speed of the front powder becomes linear. a step of extracting from the linear region of the heat generating agent / heating aids ratio as the target weight ratio, and determining a heating agent / heating aids ratio of the front powder to target mass ratio, only containing, heating agent / heating aid In the point graph showing the correspondence between the ratio and the melting rate of the front powder, the correspondence between the exothermic agent/heating aid ratio and the melting rate of the front powder when the following conditions (1) and (2) are both satisfied: A method of designing a front powder is provided, characterized in that the relationship is linear .
(1) The distance in the axial direction of the melting rate of the front powder between the approximate line of three or more points P1 and each point P1 is a value within the range of ±1 (sec). Point P1 shows the correspondence between the ratio of exothermic agent/exothermic agent and the melting rate of the front powder.
(2) The slope of the approximate straight line at the point P1 is 10 to 30.

Here, the content of the exothermic agent may be 12% by mass or more.

Further, the target melting rate of the front powder may be any value of 20 to 25 seconds.

Further, the target mass ratio may be any value of 1.0 to 1.3.

Further, the exothermic agent may include any one or more materials selected from the group consisting of Ca-Si alloy and metallic Si.

Further, the exothermic aid may contain iron oxide.

According to another aspect of the present invention, there is provided a method for producing a front powder, which comprises producing a front powder having an exothermic agent/exothermic aid ratio determined by the above-mentioned front powder designing method. ..

As described above, according to the present invention, the exothermic agent/exothermic aid ratio corresponding to the target melting rate of the front powder is extracted from the linear region. Here, in the linear region, the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate of the front powder is linear. Therefore, the exothermic agent/exothermic aid ratio corresponding to the target melting rate can be uniquely specified within the linear region. Then, according to the present invention, this exothermic agent/exothermic aid ratio is defined as the exothermic agent/exothermic aid ratio of the front powder. Therefore, the melting rate of the front powder can be adjusted to a specific target melting rate. Furthermore, according to the present invention, the melting rate of the front powder can be adjusted to the target melting rate without depending on the melting rate adjusting agent. Therefore, according to the present invention, the melting rate of the front powder can be adjusted to a specific target melting rate at low cost.

6 is a point graph showing the correspondence relationship between the melting rate of the front powder and the heat generating agent/heat generating auxiliary agent ratio when the mass% of the heat generating agent is 12 mass %. 6 is a point graph showing the correspondence relationship between the melting rate of the front powder and the heat generating agent/heat generating auxiliary agent ratio when the mass% of the heat generating agent becomes 13 mass %. 7 is a point graph showing the correspondence relationship between the melting rate of the front powder and the heat generating agent/heat generating auxiliary agent ratio when the heat generating agent mass% is 16 mass %. 6 is a point graph showing the correspondence relationship between the melting rate of the front powder and the heat generating agent/heat generating auxiliary agent ratio when the mass% of the heat generating agent becomes 20 mass %. 7 is a point graph showing the correspondence relationship between the melting rate of the front powder and the heat generating agent/heat generating auxiliary agent ratio when the heat generating agent mass% is 11 mass %. It is a side sectional view showing a schematic structure of a test device for measuring the melting rate of front powder.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the drawings, constituent elements having substantially the same functional configuration are designated by the same reference numerals, and a duplicate description will be omitted.

<1. Examination by the Inventor>
The present inventor diligently studied a technique capable of adjusting the melting rate of the front powder to a specific target melting rate at low cost, and as a result, arrived at the method of designing the front powder according to the present embodiment. Therefore, first, the examination by the present inventor will be described.

The present inventor first focused on the above-mentioned heat-generating agent and heat-generating aid as components of the front powder. The exothermic agent is a material that generates heat by being oxidized by the exothermic aid. The exothermic agent is, for example, a Ca-Si alloy, metallic Si, or the like. The exothermic aid is, for example, iron oxide or the like. The iron oxide is, for example, Fe ₂ O ₃ , FeO, Fe ₃ O ₄ or a mixture thereof.

Then, the present inventor conducted the following experiment using a Ca—Si alloy as the exothermic agent and iron oxide as the exothermic aid. That is, the present inventor fixed the mass% of the exothermic agent (mass% with respect to the total mass of the front powder) at 12 mass% and changed the content of the exothermic agent to obtain the exothermic agent/exothermic agent. We made several types of front powders with different ratios. Here, the exothermic agent/exothermic aid ratio is a mass ratio of the exothermic agent and the exothermic agent (more specifically, a value obtained by dividing the mass of the exothermic agent by the mass of the exothermic agent). Table 1 shows the composition of each front powder. In Table 1, “TC” indicates the total amount of carbon, and C/S is the mass ratio of CaO and SiO ₂ . Further, the mass% of the chemical components of the front powder and the exothermic aid are mass% with respect to the total mass of the front powder.

Then, the melting rate of each front powder was measured by the following steps. First, the electric furnace 100 shown in FIG. 6 was prepared. The electric furnace 100 includes a bottom portion 10, a heat insulating plate 20 that covers an upper portion of the bottom portion 10, and a through hole 20 a formed in the heat insulating plate 20. The crucible 30 is inserted into the through hole 20a. The crucible 30 is held in the through hole 20a. A recess 10a is formed in the bottom portion 10, and a plurality of heating elements 10b are formed on the side surfaces of the recess 10a. In the electric furnace 100, the plurality of heating elements 10b generate heat, so that the crucible 30 can be unidirectionally heated from below. The heat insulating plate 20 suppresses heat radiation from the bottom portion 10. Therefore, the heat generated from the heating element 10b is transferred from the bottom portion 10 to the crucible 30.

The measuring method of the melting rate using this electric furnace 100 is as follows. First, the heat insulating material 20 covered the concave portion 10 a of the bottom portion 10. Here, the through hole 20a of the heat insulating material 20 is arranged above the recess 10a. Then, the heating element 10b was caused to generate heat to heat the internal temperature of the recess 10a to about 1750°C. Then, the crucible 30 was inserted into the through hole 20a and held in the through hole 20a. In this state, a predetermined temperature stabilization time was waited.

Then, 5 g of the front powder 200 produced above was put into the crucible 30. Then, the time from the completion of charging the front powder 200 to the complete melting of the front powder was measured. Here, the melting of the front powder 200 was visually confirmed. Then, the measured time was taken as the melting rate of the front powder. Thus, in the present embodiment, the melting rate of the front powder is defined as the time required for 5 g of the front powder to completely melt under the heating temperature of 1750°C. In the actual continuous casting process, the temperature of the molten steel surface becomes about 1500°C. However, under the present measurement conditions, the heating temperature was set to 1750° C. in consideration of a decrease in the temperature of the crucible when the front powder was added.

Then, a point graph showing the correspondence relationship between the ratio of the exothermic agent/exothermic aid and the melting rate of the front powder was prepared. A dot graph is shown in FIG. The horizontal axis (x axis) in FIG. 1 represents the ratio of the exothermic agent/exothermic aid (that is, Ca-Si/iron oxide ratio), and the vertical axis (y axis) represents the melting rate (sec). Further, a point P1 shows a correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate.

As a result, it was found that the relationship between the exothermic agent/exothermic aid ratio and the melting rate of the front powder is linear when the exothermic agent/exothermic aid ratio is 0.8 to 1.3. Here, “linear” means that the following conditions (1) and (2) are both satisfied.
(1) The distance in the y-axis direction between each of the points P1 and the approximate straight line of the three or more points P1 is a value within the range of ±1 (sec). Here, the distance in the y-axis direction between the approximated curve and the point P1 is obtained by the following method. That is, a straight line passing through the point P1 and perpendicular to the x-axis is drawn. Then, the intersection of this straight line and the approximate straight line is obtained. Then, the y coordinate value of the intersection is subtracted from the y coordinate value of the point P1. As a result, the distance in the y-axis direction between the approximate curve and the point P1 is obtained. Therefore, in this embodiment, the distance may be a positive value or a negative value.
(2) The slope of the approximate straight line at the point P1 is 10 to 30. The inclination is preferably 12 to 26.

The straight line L1 in FIG. 1 shows an example of an approximate straight line. The approximate straight line may be obtained by any method, but here, it is obtained by the least squares method. Then, in FIG. 1, the conditions (1) and (2) are satisfied when the ratio of the exothermic agent/exothermic aid is 0.8 to 1.3. Specifically, when the exothermic agent/exothermic aid ratio is 0.8 to 1.3, the distance in the y-axis direction between the approximate straight line and each P1 is a value within the range of ±1 (sec), The slope of the approximate straight line at the point P1 is 10-30.

Therefore, when the ratio of the exothermic agent/exothermic aid is 0.8 to 1.3, the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate of the front powder becomes linear. Hereinafter, the range of the exothermic agent/exothermic aid ratio when the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate of the front powder is linear is also referred to as a "linear region". In the case of FIG. 1, the range of the linear region is 0.8 to 1.3. In this linear region, the points on the approximate straight line indicate the ratio of exothermic agent/exothermic aid to the melting rate of the front powder. Therefore, by using the approximate straight line in the linear region, the ratio of the exothermic agent/exothermic aid to the melting rate of the front powder can be uniquely specified in the linear region. Hereinafter, the approximate straight line in the linear region is also referred to as a “melting rate corresponding straight line”.

Next, the present inventor fixed the mass% of the exothermic agent at 13 mass %, and conducted the same test as above. Table 2 shows the composition of the front powder used at this time.

Further, FIG. 2 shows a dot graph showing the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate. The meanings of the horizontal axis, the vertical axis, and the point P1 are the same as in FIG. The straight line L2 is an example of the approximate straight line described above. As is clear from FIG. 2, the conditions (1) and (2) are satisfied when the ratio of the exothermic agent/exothermic aid is 0.8 to 1.8. Specifically, when the exothermic agent/exothermic aid ratio is 0.8 to 1.8, the distance in the y-axis direction between the approximate straight line and each P1 is a value within the range of ±1 (sec), The slope of the approximate straight line at the point P1 is 10-30. Therefore, even when the mass% of the exothermic agent is 13 mass %, the linear region is formed, and the range of the linear region is 0.8 to 1.8. Further, the straight line L2 is a straight line corresponding to the melting rate.

Next, the present inventor fixed the mass% of the exothermic agent at 16 mass% and conducted the same test as above. Table 3 shows the composition of the front powder used at this time.

Furthermore, a dot graph showing the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate is shown in FIG. The meanings of the horizontal axis, the vertical axis, and the point P1 are the same as in FIG. The straight line L3 is an example of the approximate straight line described above. As is clear from FIG. 3, the conditions (1) and (2) are satisfied when the ratio of the exothermic agent/exothermic aid is 0.6 to 1.8. Specifically, when the ratio of the exothermic agent/exothermic aid is 0.6 to 1.8, the distance in the y-axis direction between the approximate straight line and each P1 is a value within the range of ±1 (sec), The slope of the approximate straight line at the point P1 is 10-30. Therefore, even when the mass% of the exothermic agent is 16 mass %, the linear region is formed, and the range of the linear region is 0.6 to 1.8. Further, the straight line L3 is a straight line corresponding to the melting rate.

Next, the present inventor fixed the mass% of the exothermic agent at 20 mass %, and conducted the same test as above. Table 4 shows the composition of the front powder used at this time.

Further, a dot graph showing the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate is shown in FIG. The meanings of the horizontal axis, the vertical axis, and the point P1 are the same as in FIG. The straight line L4 is an example of the above-mentioned approximate straight line. As is clear from FIG. 4, the conditions (1) and (2) are satisfied when the ratio of the exothermic agent/exothermic aid is 1.0 to 2.0. Specifically, when the exothermic agent/exothermic aid ratio is 1.0 to 2.0, the distance in the y-axis direction between the approximate straight line and each P1 is a value within the range of ±1 (sec), The slope of the approximate straight line at the point P1 is 10-30. Therefore, even when the mass% of the heat generating agent is 20 mass %, the linear region is formed, and the range of the linear region is 1.0 to 2.0. Further, the straight line L4 is a straight line corresponding to the melting rate.

Next, the present inventor fixed the mass% of the exothermic agent at 11 mass %, and conducted the same test as above. Table 5 shows the composition of the front powder used at this time.

Furthermore, a point graph showing the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate is shown in FIG. The meanings of the horizontal axis, the vertical axis, and the point P1 are the same as in FIG. The straight line L5 is an example of the above-described approximate straight line. As is clear from FIG. 5, when the mass% of the exothermic agent is 11 mass %, the linear region is not formed. The condition (1) is satisfied when the ratio of the exothermic agent/exothermic aid is 1.0 to 2.3. However, since the slope of the approximate straight line is less than 10, the condition (2) is not satisfied.

As described above, the present inventors have found that the linear region is formed when the mass% of the exothermic agent is 12 mass% or more. Further, it was also found that the range of the linear region and the shape of the straight line corresponding to the melting rate varied depending on the mass% of the exothermic agent. In particular, the range of the linear region (in other words, the length of the straight line corresponding to the melting rate) becomes long when the mass% of the exothermic agent is 13 mass% or more.

In this linear region, the point on the straight line corresponding to the melting rate shows the ratio of the exothermic agent/exothermic aid to the melting rate of the front powder. Therefore, it was also found that in the linear region, the ratio of the exothermic agent/exothermic aid to the melting rate of the front powder can be uniquely specified. The present inventor has conceived a front powder designing method, a front powder manufacturing method, and a front powder according to the present embodiment based on such knowledge. The present embodiment will be described below.

<2. Front powder design method>
(2-1. First step)
Next, a method for designing the front powder according to this embodiment will be described. According to this design method, the ratio of the exothermic agent/exothermic aid to the target melting rate of the front powder can be uniquely specified within the linear region.

In the first step, the exothermic agent used for the front powder, specifically, the exothermic agent and the exothermic aid are specified. Here, the exothermic agent is a material that is oxidized by the exothermic aid. As the heat generating agent, any material can be used as long as it is a material used as a heat generating agent for the front powder. Preferred examples of the exothermic agent are Ca-Si alloy and metallic Si. The reason for this is as follows. That is, the Ca-Si alloy is an alloy composed of the same elements as CaO and SiO ₂ which are the main components of the front powder. Therefore, even if the front powder contains a Ca-Si alloy, the Ca-Si alloy does not significantly affect the characteristics of the front powder. The same applies to metal Si.

The exothermic aid is a material that promotes heat generation of the exothermic agent by oxidizing the exothermic agent. The exothermic aid is, for example, iron oxide or the like. The iron oxide is, for example, Fe ₂ O ₃ , FeO, Fe ₃ O ₄ or a mixture thereof. Of course, the exothermic aid is not limited to these examples. That is, in the present embodiment, any material can be used as long as it is a material used as a heat generation aid for the front powder.

(2-2. Second step)
Then, the linear region corresponding to the identified exothermic agent and exothermic aid is identified. Further, an approximate straight line in the linear region, that is, a straight line corresponding to the melting rate is prepared. The specific processing contents are described in 1. It is as explained in. The outline is as follows. That is, by fixing the mass% of the exothermic agent to any value of 12 mass% or more and changing the content of the exothermic agent, a plurality of types of front powders having different exothermic agent/exothermic agent ratios can be obtained. Create.

Then, the melting rate of each front powder is measured. The specific measuring method is as described above. Then, a dot graph showing the correspondence relationship between the ratio of the exothermic agent/exothermic aid and the melting rate of the front powder is prepared. Then, the linear region is specified based on this point graph. Specifically, the range of the exothermic agent/exothermic aid ratio that satisfies the above-described conditions (1) and (2) is specified, and this range is defined as the linear region. Further, the approximate straight line calculated when the linear region is specified is set as the melting rate corresponding straight line. Through the above steps, the linear region is specified and the straight line corresponding to the melting rate is produced.

Here, the range of the linear region and the shape of the straight line corresponding to the melting rate vary depending on the mass% of the exothermic agent. In particular, the range of the linear region (in other words, the length of the straight line corresponding to the melting rate) becomes wide when the mass% of the exothermic agent is 13 mass% or more. Further, as will be described later, the target melting speed of the front powder is often set to 20 to 25 seconds. When the mass% of the exothermic agent is 13 mass% or more, the melting rate correspondence straight line includes a point corresponding to 20 to 25 seconds. Therefore, when the target melting rate is 20 to 25 seconds, the exothermic agent/exothermic aid ratio corresponding to the target melting rate can be uniquely specified. Therefore, the mass% of the exothermic agent is preferably 13 mass% or more.

The upper limit of the mass% of the exothermic agent is not particularly limited, but is preferably 20 mass%. When the mass% of the exothermic agent exceeds 20 mass%, the mass% of the exothermic agent in the front powder may become very large. For example, depending on the value of the exothermic agent/exothermic aid ratio, nearly half of the total mass of the front powder may be occupied by the exothermic agent and the exothermic assistant. In this case, it may be difficult to adjust other components (such as SiO ₂ described later) for realizing the function as the front powder. Therefore, the upper limit of the mass% of the exothermic agent is preferably 20 mass %.

Further, since the range of the linear region and the shape of the straight line corresponding to the melting rate may differ for each combination of the exothermic agent and the exothermic agent, it is preferable to perform the second step for each combination of the exothermic agent and the exothermic agent. .. In addition, once the second step is performed, the result of the second step can be reused unless the combination of the exothermic agent and the exothermic aid is changed. Also, a material that is difficult to dissolve in the front powder may be included in the front powder. In this case, the range of the linear region and the shape of the straight line corresponding to the melting rate may vary depending on the type of these materials and the amount of the powder added to the front powder. Therefore, it is preferable to perform the second step for each type of the material and the amount of the material added to the front powder.

(2-3. Third step)
In the third step, the exothermic agent/exothermic aid ratio corresponding to the target melting rate of the front powder is extracted from the linear region as the target mass ratio. Specifically, the point corresponding to the target melting rate is extracted from the straight line corresponding to the melting rate, and the exothermic agent/exothermic aid ratio indicated by this point is set as the target mass ratio.

Here, the target melting speed of the front powder fluctuates according to the specifications required for the front powder, but is often set to any value of 20 to 25 sec. When the melting rate of the front powder is any value of 20 to 25 seconds, continuous casting can be stably performed, and the exposed surface of the molten steel is often suppressed.

Further, the target mass ratio differs depending on the mass% of the exothermic agent and the target melting rate. For example, when the mass% of the exothermic agent is any value of 13 to 20 mass% and the target melting rate is any value of 20 to 25 sec, the target mass ratio is according to the straight lines L2 to L4. It will be any value from 1.0 to 1.3. In other words, when the mass% of the exothermic agent is any value of 13 to 20 mass% and the target mass ratio is any value of 1.0 to 1.3, the melting rate of the front powder is 20. It is uniquely set to any value of ˜25 sec. In Patent Document 1, the exothermic agent/exothermic aid ratio is 1.67% by mass or less. In Patent Document 2, the mass% of the exothermic agent is 5 mass% or less. Therefore, both the exothermic agent/exothermic aid ratio described in the cited document 1 and the mass% of the exothermic agent described in the cited document 2 set the melting rate of the front powder to any value of 20 to 25 sec. Is different from the required value for.

Further, as described above, the shape of the straight line corresponding to the melting rate differs depending on the mass% of the exothermic agent. Therefore, the point corresponding to the target melting rate may not be extracted from the melting rate corresponding line. For example, when the mass% of the exothermic agent is 12 mass %, the melting rate correspondence straight line does not include the point corresponding to 20 to 25 seconds. Therefore, when the target melting rate is 20 to 25 seconds, the exothermic agent/exothermic aid ratio corresponding to the target melting rate cannot be specified. In this case, the mass% of the exothermic agent is changed and the second step is performed again. Then, the point corresponding to the target melting rate may be extracted from the newly prepared straight line corresponding to the melting rate.

(2-4. Fourth step)
In the fourth step, the exothermic agent/exothermic aid ratio of the front powder is determined to be the target mass ratio. Through the above steps, the parameter (heat generating agent/heat generating auxiliary agent ratio in the present embodiment) necessary for setting the melting rate of the front powder to the target melting rate is determined. Therefore, in this embodiment, the melting rate of the front powder can be adjusted to the target melting rate without depending on the melting rate adjusting agent. Further, conventionally, when the melting speed of the front powder is different from the target melting speed, the components of the front powder have been manually adjusted while using the front powder in continuous casting (or performing some kind of melting test). According to this method, it takes a lot of time and cost to adjust the melting speed of the front powder. In this respect, in the present embodiment, the melting rate of the front powder can be adjusted to the target melting rate at the designing stage of the front powder. Therefore, according to this embodiment, the melting rate of the front powder can be adjusted to a specific target melting rate at low cost.

(2-5. Fifth step)
In the fifth step, parameters other than the exothermic agent/exothermic aid ratio are determined. First, the mass% of the exothermic agent is determined based on the mass% of the exothermic agent and the exothermic agent/exothermic agent ratio. Next, the type and mass% of the other components of the front powder are determined. The types of components contained in the front powder are not particularly limited as long as they can be contained in conventional front powders.

The components and mass% that can be contained in the front powder according to the present embodiment are as follows, for example.
T. C:0≦T. C≦5
SiO ₂ : 20≦SiO ₂ ≦50
Al ₂ O ₃ :0≦Al ₂ O ₃ ≦15
Fe ₂ O ₃ :5≦Fe ₂ O ₃ ≦25
Incidentally, Fe ₂ O ₃ in this case, the heat generating agent described above is not counted.
CaO: 20≦CaO≦50
Na ₂ O: 0≦Na ₂ O≦15
F: 0≦F≦15
MgO: 0≦MgO≦15
CaO/SiO ₂ : 0.3≦C/S≦2.0
Li ₂ O: 0≦Li ₂ O≦15
The front powder is designed through the above steps.

<3. Front powder manufacturing method>
In this embodiment, the front powder is manufactured according to the contents designed by the above-described design method. This makes it possible to produce a front powder that melts at the target melting rate.

<4. Front powder>
The front powder according to the present embodiment is the front powder manufactured by the manufacturing method described above. This front powder melts at the target melting rate. For example, when the target melting rate is any value of 20 to 25 seconds and the mass% of the exothermic agent is 13 mass% or more, the exothermic agent/exothermic aid ratio is 1.0 to 1.3. It becomes the value of. The front powder is applicable to continuous casting of various molten steels (for example, ultra-low carbon steel, low-carbon steel, medium carbon steel, and high-carbon steel), but continuous casting of other types of molten metal is also possible. Of course, it may be applied to casting.

Next, the following examples were performed in order to confirm that the front powder designed according to the present embodiment melts as designed in continuous casting. Specifically, prepared Ca-Si alloy as the heating agent was prepared _Fe 2 _{O 3} as a heating aid. Then, by fixing the mass% of the exothermic agent to 13 mass% and changing the content of the exothermic agent, the exothermic agent/exothermic agent ratio is 1.51, 1.23, 1.12, 1. A plurality of types of front powders having 0.000 and 0.80 were produced. Here, when the ratio of the exothermic agent/exothermic aid is 1.23, 1.12, and 1.00, the melting speed of the front powder is 25, 23, and 20 seconds according to the above-described approximate straight line L2. .. On the other hand, when the ratio of the exothermic agent/exothermic aid is 1.51, according to the above-mentioned approximate straight line L2, the melting speed of the front powder becomes larger than 25 sec. Further, when the ratio of the exothermic agent/exothermic aid is 0.80, the melting rate of the front powder is less than 20 sec according to the above-mentioned approximate straight line L2.

Next, ultra low carbon steel was continuously cast using the above-mentioned front powder. Then, on the assumption that the front powder melts at a melting rate of 20 to 25 seconds, the amount of the front powder added was determined. Then, the determined amount of mold powder was charged from above the mold. As a result, when the ratio of exothermic agent/exothermic aid is 1.23, 1.12, 1.00, the front powder melts smoothly, and a sufficient amount of slag gets between the mold and the bottom slab. It is. Also, after confirming that the liquid level of the slag has dropped to a preset level, the main body powder was put in from above the mold, but after the liquid level of the slag dropped to the preset level, the main body powder was put in. The molten steel surface was never exposed. As a result, continuous casting could be stably performed. Specifically, the bottom slab did not have a problem such as double skin. There was also no deckle formation during operation. Therefore, when the ratio of the exothermic agent/exothermic aid is 1.23, 1.12, and 1.00, the front powder is melted at the above-mentioned melting rate. On the other hand, when the ratio of the exothermic agent/exothermic aid was 1.51, the melting speed of the front powder was slow. Therefore, a sufficient amount of slag could not enter between the mold and the bottom slab. Therefore, double skin was formed on the bottom slab. Also, when the ratio of exothermic agent/exothermic aid is 0.80, the melting speed of the front powder is too fast, and the molten steel surface is exposed before the main body powder is charged, and formation of deckle is confirmed on the molten steel surface. It was

Therefore, it was found that the front powder designed according to this embodiment melts as designed (that is, at the target melting rate) in continuous casting. Similar effects were obtained in continuous casting of low carbon steel, medium carbon steel, and high carbon steel.

The preferred embodiments of the present invention have been described above in detail with reference to the accompanying drawings, but the present invention is not limited to these examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

10 Bottom 20 Heat Insulation Plate 20a Recess 30 Crucible 100 Electric Furnace Equipment 200 Mold Powder

Claims (7)

A method of designing a front powder comprising a heat-generating agent and a heat-generating auxiliary agent for oxidizing the heat-generating agent,
The range of the exothermic agent/exothermic aid ratio is linear when the correspondence relationship between the exothermic agent/exothermic aid ratio, which is the mass ratio of the exothermic agent and the exothermic aid, and the melting rate of the front powder is linear. And the process specified as
Extracting the exothermic agent/exothermic aid ratio corresponding to the target melting rate of the front powder from the linear region as a target mass ratio,
Determining the exothermic agent/exothermic aid ratio of the front powder to the target mass ratio,
In a point graph showing the correspondence relationship between the exothermic agent/exothermic aid ratio and the melting rate of the front powder, the exothermic agent/exothermic aid ratio is satisfied when the following conditions (1) and (2) are both satisfied: And the melting rate of the front powder is linear, the front powder designing method.
(1) The distance in the axial direction of the melting rate of the front powder between the approximate straight line of three or more points P1 and each point P1 is a value within the range of ±1 (sec). Point P1 shows the correspondence between the ratio of the exothermic agent/exothermic agent and the melting rate of the front powder.
(2) The slope of the approximate straight line at the point P1 is 10 to 30. The front powder design method according to claim 1, wherein the content of the exothermic agent is 12% by mass or more. The front powder designing method according to claim 1 or 2, wherein the target melting rate of the front powder is any value of 20 to 25 seconds. The front powder designing method according to claim 3, wherein the target mass ratio has a value of 1.0 to 1.3. The said exothermic agent contains any 1 or more types of material selected from the group which consists of Ca-Si alloy and metallic Si, The front powder of any one of Claims 1-4 characterized by the above-mentioned. Design method. The method for designing a front powder according to claim 1, wherein the heat-generating aid contains iron oxide. A method for producing a front powder, comprising producing a front powder having the exothermic agent/exothermic aid ratio determined by the method for designing a front powder according to any one of claims 1 to 6.

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